What's the drawback to a truss Dob?

[ksodbartman]

After a year of ETX-ville, I'm looking to move to a more upscale town. While I thought I was headed for LX Town, I happened to pass Truss Dob City. If I can get a 12" Truss Dob for the price of an ETX-125 (http://riverscamera.com/lightbridge.html), why shouldn't I go for it?

There's gotta be a catch, but I don't know enough about truss Dobs to know what it is...

[aurora]

There are two general types of Dobs, truss and tube. A 12 inch is about at the border where trusses are generally preferred. As the mirrors get bigger, the tube of a traditional dob gets too big to be easily moved, so people go to a truss -- a big scope that takes up only a little storage space. The downside to a truss is that it takes a little longer to set up, a tube dob is dead simple to set up, just set the tube on the base. They both need to have the collimation checked because they are Newtonians.

I have yet to see one of the new Meade truss scopes, so I cannot comment on how they compare to the competition.

Is that what you wanted to know?

[ksodbartman]

How involved is checking the collimation? Is it a simple task?

Do trusses usually come with Autostar or something similar?

My first print astrophotos had star trails because it was alt/az aligned instead of polar. Wil the truss have the same problem? It doesn't look like you can polar-align that puppy...

[aurora]

Do trusses usually come with Autostar or something similar?



No, Dobs do not track at all. No computer. No motor. As John Dobson use to say, it runs on gravity and yogurt. Gravity holds it together, and you eat the yogurt to provide energy to move it around. :whistle:

This is true for all Dobs, whether they have a truss or not.

The Dob gives you the most bang for the buck for observing deep sky objects, because the money goes into the optics (primary and secondary mirror) and the mount is simple and cheap, and there is no need for motors or electronics. The disadvantage is, well, it has no motors or electronics.

Some of us like it that way! :lol:

So how do you find stuff without a computer? Starhopping! A red dot or telrad finder to get started, then either a good sky chart or a planetarium software program that shows the night sky and lets you zoom in.

Collimation takes a little practice but eventually becomes second nature. I might spend 5 minutes on it when I move the scope in my truck. Look in other messages in this topic in BAUT, and you will find where others have posted links to web sites that give instructions for collimation.

[Kaptain K]

My first print astrophotos had star trails because it was alt/az aligned instead of polar. Wil the truss have the same problem?
Yes.

It doesn't look like you can polar-align that puppy...
Correct! By definition, a dob is an alt-az mount. An alt-az mount cannot be polar-aligned, unless it is at one of the poles. The only scopes that can be polar-aligned are those on an equatorial mount.

There are "work-arounds" for astro-imaging with an alt-az mount. You take a bunch of short exposures (short enough that the star trails dont show) and "stack" them together with a program like Registax.

[Dave Mitsky]

Just to make it perfectly clear, truss-tube Dobs must be collimated each and every time they are assembled.

Starmaster Sky Tracker Dobs and Obsession Dobs having ServoCAT drives have both stepper motor drives and GoTo capability. This capability does not come cheaply. The Dob Driver II can be added to other Dobs fairly inexpensively. An equatorial (Poncet) platform is another option.

Long exposure astrophotography can be achieved with either one of these types of drives. See previous posts on this topic for links that I provided.

Dave Mitsky

[Fr. Wayne]

Being way up in Minnesota you could experiment with base being placed on a 40 degree inclined sub-base which could, and it's a big could, mechanically rotate once per 24 hour spin, and post how to make a "ksodbartman" to Canadien dobsters. Forget about trying to make a profit though. Even at 17% over cost you'd sell only a dozen. South of you the sub-base would be too unstable.